1. Field of the Invention
The subject invention generally relates to a coating composition and, more particularly, to a coating composition including a high molecular weight polycarbodiimide which forms a coating having excellent physical properties.
2. Description of the Related Art
Polycarbodiimides and compositions including polycarbodiimides are generally known in the art. Polycarbodiimides include repeating structuring units represented by R—N═C═N—R, where R is an independently selected organic group, such as an aromatic group.
Methods of producing polycarbodiimides are also known in the art. In conventional methods of producing polycarbodiimides, an organic isocyanate, such as an aromatic isocyanate, is polymerized in the presence of a carbodiimidization catalyst. Generally, the organic isocyanate is polymerized in the presence of the carbodiimidization catalyst while disposed in a solvent such that the polycarbodiimide is produced in solution.
However, in conventional methods of producing polycarbodiimides in solution, the polycarbodiimides precipitate and/or gel in the solvent once the polycarbodiimides reach a certain molecular weight, which is typically from 1,000 to 3,000. Once the polycarbodiimides precipitate and/or gel in the solvent, polymerization generally ceases such that the molecular weight of the polycarbodiimide does not increase. As such, polycarbodiimides produced via conventional methods have relatively low molecular weight, which significantly decreases potential applications in which the polycarbodiimides may be utilized in view of the physical properties obtainable from such polycarbodiimides. Specifically, the molecular weight of the polycarbodiimides impacts the physical properties of the polycarbodiimides.
In addition, because polycarbodiimides precipitate in conventional methods of producing polycarbodiimides, these polycarbodiimides cannot be stored, transported or processed in solution. Rather, the polycarbodiimides produced via conventional methods are processed in powder form. The powder form of the polycarbodiimides is generally obtained from isolating the polycarbodiimides that have precipitated and/or gelled in the solution. Such polycarbodiimides often have thermosetting properties when heated to a certain temperature (e.g. greater than 180° C.), which further limits applications in which the polycarbodiimides may be utilized.
More specifically, because conventional polycarbodiimides generally have a limited molecular weight, conventional coatings formed from conventional polycarbodiimides also suffer from disadvantages relative to their physical properties. Accordingly, alternatives to such conventional polycarbodiimides are generally utilized in coating compositions, such as epoxy resins and/or polyamides. These alternatives have traditionally provided conventional coatings having improved physical properties as compared to conventional polycarbodiimide coatings. However, such alternatives are expensive.